Antenna



P. semi-ER Oct. 21, 1952 ANTENNA 3 Sheets-Sheet 1 Filed Jan. 9, 1946 INVENTOR PH/u/p 6. @4275? BY wgm ATTORN EY P. s." CARTER Oct. 21, 1952 .3 ,Sheet-Sheet 2 Filed Jan. 9, 1946 INVENTOR pH/ZL/P 52 (AFTER ATTORNEY Patented Oct. 21, 1952 ANTENNA Philip S. Carter, Port Jefferson, N. Y., assignor to Radio Corporation of America, a. corporation of Delaware Application January 9, 1946, Serial No. 639,998

3 Claims.

The present invention relates to ultra short wave antennas and, more particularly, to loop antennas having dimensions large in terms of the operating wavelength.

An object of the present invention is the improvement of the band width of antennas.

Another object of the invention is improving the efficiency of short wave antennas.

Still another object of the present invention is the provision of an antenna which may be mounted on an airplane without presenting objectionably large wind resistance.

A further object of the present invention is the provision of an airplane antenna which is less hazardous to ground crew personnel than previously known types.

Still a further object of the present invention is the provision of an antenna which, if desired, produces a non-directional radiation pattern for broadcasting use.

Still a further object of the present invention is the provision of an antenna which'is mechanically stable and electrically grounded.

Still another object of the present invention is the provision of a loop antenna which may be energized from a transmitter by a coaxial line without the use of line balance converters or similar matching structures.

The foregoing objects and others which may appear from the following detailed description are attained by providing a loop antenna, having a circumference of the order of one or a few wave-lengths at the operating frequency. The loop is preferably a single turn arrangement using a large diameter conductor. The antenna may be coupled to a coaxial transmission line and the antenna itself may utilize elements of the said coaxial transmission line as elements of the loop construction. In a modified form a half loop working against a metallic ground plane may be employed.

The present invention will be more fully understood by reference to the following detailed description which is accompanied by a drawing in which:

Fig. 1 illustrates in simplified diagrammatic form an embodiment of the present invention, while Fig. 2 illustrates a modification of the form of construction shown in Fig. I, particularly useful for broadcasting use.

Fig. 3 illustrates a further modification of the invention wherein a plurality of horizontal loops are vertically stacked to produce a more uniform radiation pattern in-the horizontal plane;

Fig. 7 illustrates a further modification of Fig.

6 whereby the band width of the antenna is increased.

Figs. 8, 9 and 10 illustrate further modifications of the method of feeding the antennas of Fig. 6.

Fig. 11 is a perspective view of a horizontal loop antenna and the reference axes radiating from the antenna useful in understanding the following figures.

Fig. 12 is a diagrammatic representation of the current distribution of a loop antenna utilizing the principles of the present invention.

Fig. 13 is a curve illustrating the relationship of the voltage induced in a receiving loop antenna versus the circumference of the loop in terms of operating wavelength.

Fig. 14 is a curve illustrating the relationship between the induced voltage in a loop antenna and the circumference of the loop for energy arriving along a direction perpendicular to the plane of the loop, while Fig. 15 illustrates the horizontal and vertical directivity patterns of a horizontal loop antenna, utilizing the principles of the present invention.

Fig. 16 is a further field strength pattern of the present invention, and

Fig. 17 is a family of curves illustrating the relationship between the radiation resistance of a loop antenna versus the loop circumference in wavelengths.

Referring now to Fig. 1, there is shown a method of feeding a loop antenna which is large in terms of the operating wavelength, from a single coaxial line. Transmission line TL includes an outer sheath [0 and an inner conductor ll. At point X the transmission line TL is bent around substantially half the circumference of a circle. For the remainder of the circumference of the circle a conductor I2 is provided having the same diameter as sheath l9 and electrically connected to sheath ill at point X. At a point on the circumference of the circle opposite point X where conductor I2 and outer sheath iii are in end to end relationship, the inner conductor I l of the transmission line TL extends beyond sheath I 9 and is connected to the end of conductor l2. Thus, distances a and b are equal and the opposing ends of conductor l2 and sheath ID are equi-distant from a point of zero reference potential as may be represented by point X. Therefore, radio frequency energy, unbalanced with respect to ground, flowing in line TL may be used to energize the antenna.

The radiation pattern of the loop antenna of Fig. 1 varies somewhat with the dimensions of the loop in terms of the operating wavelength. The effect of variations in the dimensions will be discussed later with reference to following figures and mathematical developments. However, it may be remarked atthis pointv that tests of the loop of Fig. 1 show comparatively small variations of impedance over a wide. frequency band.

In case it is desired to radiate energy substantially uniformly in a horizontal plane, the construction shown in Fig. 2 may be used. Transmission line TL in Fig. 2 feeds the loop antenna generally similar in construction to that shown in Fig. 1 and similar elements have similar reference characters applied thereto. However, at point X the antenna of Fig. 2 is bent at right angles so that transmission line TL is vertical while the plane of the loop itself is horizontal. At the adjacent ends of outer sheath I and conductor l2, conductive vertical supporting posts 20 and 22 are provided. All: three supports, that is line TL and posts 20, 22 are connected at their lower ends to the metallic ground plane 18. The length of the supporting means for the antenna are so chosen as to be equal to an odd multiple of a. quarter wavelength as indicated in Fig. 2.

The entire loop is effectively insulated from the ground plane 18 for operating frequency currents while at the same time, for direct current, lightning strokes etc., the entire structure may be considered grounded. The antenna of Fig. 2 has a circumference of two wavelengths at the operating frequency. The effect on the pattern of the increase in circumference will be discussed in more detail later.

Fig. 3 illustrates another construction of the loop, antenna of the present invention whereby it may be utilized for broadcast transmission or reception. Here two large diameter conductors are bent into nearly closed circles, each having a circumference of two wavelengths, thus forming loops 30 and 32. Between a pair of adjacent ends of loop 32 is connected the vertical central two wire balanced transmission line TLB by means of conductors 33 and 34 parallel to a radius of loop 32 and preferably in the plane of the loop. The balanced transmission line TLB continues vertically a distance equal to an odd multiple of a quarter wavelength to the center of loop 30. It is there connected tov the opposing ends of loop 30 by means of conductors 35, 36 parallel to a radius of loop 30. Transmission line TLB is twisted between loops 3i] and 32 so that the two radii mentioned above lie in vertical planes intersecting along the vertical axis of the antenna at an angle of forty-five degrees. Due

to the forty-five degree displacement and the phase quadrature feeding relationship obtained by the quarter wave spacing between loops 30 and 32, perfect circle distribution of the radiated energy is attained in the horizontal plane. This may be demonstrated as follows:

From one loop alone, the field E is given by the relationship E1=A cos 2, where is a measure of the angular displacement around the again perfectly circular.

center of the loop in the horizontal plane. The second loop alone gives a field E2 determined by the expression;

E2=-' -7'A cos 2(J -45)=:,:7'A sin 2 (1) Adding the two fields together, the total field is:

Et=A (cos 24;? sin 2 =Ae= (2) Therefore, the field |Er|,=A (3) ([Er] indicates the magnitude of Er) Though only one method of energizing the antenna of Fig. 3 is shown, any scheme giving a balanced feed may be used. Though the loops in Fig. 3. are. shown as having a circumference of 2A, a pair of loops having a circumference of 1A may be used, in which case, they are fed in phase quadrature, by the same method as for the 2A loop, but the feed points are now spaced around the circumference. A similar mathematical consideration shows that the field is Any number of antennas may be vertically stacked in order to obtain as much vertical directivity as desired with uniform horizontal field strength.

Fig. 4 illustrates a modified manner of feeding the. antenna of Fig. 1. Here the. transmission line TL having a. sheath In and an inner conductor II is split into two parallel connected branches 4B and 4| at point X. The two branches are bent around the circumference of a circle, branch 40 being longer than branch H by an odd multiple of a half wavelength. At the point where branches 4i] and 4| oppose each other, the inner conductors are connected together, thus in effect providing a single continuous inner ring 43 connected at point X to inner conductor ll of transmission line TL. Here again the loop antenna is energized in a balanced relationship from an unbalanced transmission line TL.

Fig. 5 illustrates a way in which a further improvement'in the band width of the antenna of Fig. 1 may be attained. Here the loop antenna itself is formed of two hollow conductive cones 45. and 46. Each is so bent that its axis is half the circumference of a circle and the cones are so arranged that theirv apexes oppose each other at 41' while at 48 base ends of the cones are electrically connected together. At point 48. a suitable supporting pipe or hollow pole 49 is provided. Supporting pole 49 is preferably hollow so that transmission line 'I'L may pass up through 49 into one of the cones, say cone 46, to its apex. There the outer conductor lllof'transmission line TL is connectedto the apex of bent cone 46. The inner conductor I I of transmission line TL passes across the gap at Hand is connectedto the apex of bent cone 45. Preferably the circumference of the loopof Fig. 5 is chosen to be a multiple of the operating wavelength at the midband of the frequency band forv which it is designed. The radiation pattern and electrical advantages of Fig. 1 are retained in the modification of'Fig. 5 with the further advantage that an increased broad band effect is also attained.

In Fig. 6 I have shown a. modified form of the present invention which is particularly useful on airplanes. The antenna comprises a conductor bent in the form of a half loop 60 having a semicircumferenceof one-half of the operating wavelength and connected at point 6| to aconductive ground sheet58. At the opposite end of the semicircumference the inner conductor ll of transmissionline TL is connected to the semi loop 60. The outer, sheath Ill of transmission line TL is connected to the ground sheet 58. Ground sheet 58 may be the outer surface of the fuselage of an airplane or it may be an upper or lower wing surface as desired.

As indicated by arrow F the antenna of Fig. 6 has a maximum of radiation in the direction along a line from the feed point toward point 6 I. However, the radiation minimum in the right angle direction is not greatly less than the maximum. Such an arrangement provides an airplane antenna having a low wind resistance. Also, due to its small extension from the surface of sheet 58, and shape, ground crew personnel are much less liable to eye and other injuries than when the common whip antenna is used. Furthermore, the smooth outline of the antenna and its small projection render it less likely to become entangled with cables which may be employed around the landing field.

The modification shown in Fig. 7 adds a sleeve feed to the antenna of Fig. 6 to widen its band width. Here the transmission line TL extends above ground sheet 58 a distance of the order of one-eighth of the operating wavelength in the form of a sleeve and an inner conductor H. The inner conductor II is directly connected in series between semi-loop 60 and inner conductor H of transmission line TL. The inner conductor ll preferably has a diameter less than the diameter of inner conductor I I. Thus, the eighth wave section comprised by ID, H is arranged to have a characteristic impedance of a value lying between the impedance of the transmission line and the impedance of semi-loop antenna. itself. Otherwise, the construction of the antenna of Fig. 7 is the same as that of Fig. 6.

Similarly, the general construction of the further modification shown in Fig. 8 resembles that shown in Fig. 6, the only distinction being in the manner of feeding the antenna. Here the inner conductor l I of transmission line TL is connected to the free end of semi-circular conductor 60. The end of conductor 60 is hollow a distance equal to approximately a quarter of the operating wavelength from the free end. Supplemental conductor 62 is concentrically arranged within the hollow portion and is connected to ground plane 58 near point of emergence of inner conductor I8 of transmission line TL and connected to semi-circular conductor 60 at the bottom of the hollow portion.

Thus a quarter wave section of transmission line is placed effectively in shunt with the antenna at the feed point. This acts as a compensation circuit to widen the frequency band. At the midband frequency where the length is exactly a quarter wavelength the impedance is infinite but when the frequency is higher than that of the midband frequency it presents a capacitive reactance in shunt with the feed point, thus compensating for the inductive reactance of the. antenna. At a frequency somewhat lower than the midband frequency the shunt line presents an inductive reactance in shunt with the antenna compensating for the capacitive reactance of the antenna.

Fig. 9 illustrates a further modification of the invention. Herein the semi-circular conductor 90 has an overall length of one quarter of the operating wavelength. Thus, the semi-loop taken in conjunction with the electrical image formed by ground plane 58 acts as a loop having a circumference of a half wavelength rather than a one wavelength circumference loop as previously described. Conductor 90 is hollow through nearly its entire length. Coaxially arranged within hollow conductor is an extension 53 of the inner conductor l l of transmission line TL. The interior quarter wave section acts as a compensation circuit to widen "the frequency band. By suitably varying the length of extension conductor 63 within conductor 90 from the point of entrance to shorting plate 64, the reactive component of the antenna may be tuned out over at least a portion of the operating band. The effect of the change in circumference upon the characteristics of the antenna will be discussed later by reference to the impedance characteristics and directivity patterns.

The half loop antenna shown in Fig. 10 is again a half wave semi-loop. The inner conductor ll of transmission line TL extends half way around the semi-circumference of the loop where it meets and is connected. to conductor 68. It is surrounded by a curved supplemental sleeve 92 insulated from both conductor 60 and ground sheet 58. Thus, the effective feed point of the loop is moved around to point I00 instead of being closely adjacent to the ground plane as in previously discussed modifications.

In the following mathematical development of the properties of large'loop antenna, it should be understood that all loops are considered to lie in a horizontal plane with the axis of the loop pointing upward; that is, along the Z axis in Fig. 11. The feed terminals are assumed to lie on the negative X axis. The radius of the loop is given by a. The spherical coordinate system shown in Fig. 11 is used to specify directions with respect to the loop antenna. The position of the feed point as shown in Fig. 11 is important since it determines the current distribution in the loop. Fig. 11 further shows the polarizations of the electric vector, namely E, and El, E0 being the electric vector of a vertically polarized wave while Ea indicates the electric vector of a horizontally polarized wave. In this application we define a vertically polarized wave as one whose magnetic vector'is horizontal, i. e. the electric vector lies in a vertical plane containing the direction of propagation or ray. The object of this definition is to avoid limiting the direction of propagation to the horizontal.

The current distribution in the loop is assumed to be sinusoidal as shown in Fig. 12. This is a close approximation to the actual distribution except at the current minimum points where the actual current is finite rather than zero. The current distribution in the loop of Fig. 12 where the circumference is one and one-quarter wavelengths is shown to be symmetrical with respect to a point opposite the feed point and is proportional to cos (Ka bo) Where a is the loop radius and (1:0 is the angle to the reference point which is taken as diametrically opposite to the feed point. Regardless of the circumference of the loop the current distribu- .if the field strength is 10 microvolts per meter and the wavelength is 2 meters, the voltage in a.

- 7 half. waveloop would be lOX2X.1205- 2'.4 1 microvolts. Curve b of Fig. 1-3 is a similar curve for a direction =90, :90 (Fig- 11). In this direction the pick-up becomes zero when the circumference of theloop is one wavelength or any odd multiple thereof while it becomes a maximum when the circumference is an even multiple of a wavelength.

The curve in Fig. 14 shows the voltage induced in a receiving loop when the wave direction is perpendicular to the plane of the loop, that is, along the axis where 0:0 and 0. Instead of using the curve of Figs. 13 and 14 for determining the voltage induced in the receiving loop, the voltage may be determined from the following equations:

First, the situation will be considered where a very small loop compared to a wavelength is used.

Let V0 be the voltage induced in. such a loop, then where where Jni'u) :the Bessel function of the first kind of order n (and argument u). In the case where the loop is an even multiple m of a wavelength in circumference, the foregoing expression be- COI'IIES I- When the wave is polarized in the horizontal plane, that is, when 0:90", the voltage becomes:

If the loop is one wavelength in circumference ('7) becomes:

while for two wavelengths in circumference, ('7) becomes the following:

!V|:[V0] 0.4478 cos 2 (9) In case'the wave is vertically polarized, the equation for the induced voltage is as follows: V=j V sin (Ktlvr) cos 0 Where the loop has a circumference which is an integral multiple (m) of a wavelength and th received wave is vertically polarized, the voltage becomes the following:

Fig. 15, curve 0, shows the horizontal field strength pattern, that is, the pattern in the plane of the antenna for a loop having a half wave circumference. It will b noted that, when the loop is used for transmitting, the radiation is greater in the direction of a diameter through the feed point. Fig. 15, curve d, shows the vertical pattern in the plane zzero, that is, with the vertical plane passing through the feed point. There is no vertically polarized field (E6) in this plane. The vertical patterns for both horizontally polarized (E and vertically polarized (Ea) radiation in the vertical plane :90 are shown in Fig. 16. In this plane, that is, the plane at right angles to that through the feed point, the horizontally polarized radiation is a maximum in the horizontal direction and zero vertically while the vertical polarized radiation E, is zero horizontally and a maximum vertically. In the regions between horizontal and vertical, the radiation is elliptically polarized since E0 and E are in phase quadrature.

Where the circumference of the loop is increased to one wavelength, the horizontal pattern is a simple figure of eight or cosine curve with maxima along the diameter passing through the feed point. The vertical pattern in the plane =0 (vertical plane passing through the feed point) is the same as that shown in Fig. 150. The radiation is a maximum in the vertical direction While the E6 (vertically polarized radiation) is zero everywhere in this plane. The vertical radiation pattern in the plane =90, that is, the vertical perpendicular to the plane passing through the feed point, is a simple figure of eight or cosine curve. All radiation is vertically polarized (E9 radiation), the horizontally polarized radiation (E being zero everywhere. It will be noted that this situation is quite different from the half wave circumference loop which radiates considerable horizontally polarized energy in this plane. Where a loop has a circumference equal to a multiple of a wavelength, the horizontal patterns are simple cos me curves where (m) is the integral multiple of the wavelength in the circumference. Thus, the figure of 8 pattern for a loop of one wave circumference becomes in the case of two wave circumference a four-leaf clover pattern.

The variation in radiation resistance with loop circumference is shown in detail in Fig. 17 for loops up to two wavelengths in circumference with the value for three wavelengths also indicated. Curve a of Fig. 1'7 indicates the total variation in radiation resistance with a variation of the loop circumference while curves b and c indicate respectively the horizontally and vertically polarized radiation resistance components of curve a. The values of the radiation resistance between two wavelengths and three wavelengths are not shown in detail but the general shape of the curve is well indicated in the area between one and two wavelengths. It should be noted that for circumferences greater than a half wavelength, the radiation resistance is of the order of that of a half-wave dipole, reaching a maximum of over ohms in the vicinity of one and one quarter wavelengths circumference. The I Fix, radiation efliciency, it will therefore be noted, is u= JL 00S aoo 005 do p very high in contrast to the extremely low efficiency of small loops. [.7 {K11 $111 9 e (o) H q t mathematical theory of D entennas 5 After changing the variable of integration, con- Whl h re large mp r t h Operatmg W Vesiderable trigonometric and algebraic manipulalength W111 new be given With reference 150 tion and making use of the well-known expan- 11 for the geometry involved. sion:

MATHEMATICAL THEORY m m K 1. Radiation fields-transmitting Z0011 expU a cos noo (MIA a Sm 0) exp (mu) Let a=loop radius, 41 the angle to the current (22) element with X axis asreference and I we obtain:

1 A 2 m a i(n+1) -m-nt E- .7 e X(Ka) sin (Ka1r)n=z m( J, .(Ka S1110) (23) Io f m i(n+1) i(n-1) EM e X(K (Km fgs .7) P (Wm-(Ker (n1) -'(Ka) (24) 21r w b where Jn (X) =Besse1 Function of nth order with Z er argument (X).

After changing to practical units, combining Assume time funct1on=Re{exp(awt)} in accordi ance with standard practice 25 terms in plus and mmus n and makmg use of the relation Let A be the magnet1c vector'potential. Gaussian units are used.

(12) where J'n' (X) is the derivative, we obtain:

1201 a Jo(Ka) sin 0) J,, (Ka sin 0) 1 E----r0 G 1 ()(Kll) 8111(Kl11f') 2 J) W005 71 (25) co 1 ht=- t wny Sin Kat 005 6 2, (j)* M Sh h volts/meter 26 n, "=1 n (Ka) V SMALL LOOP =-'KA (1 At great distances 3 When the loop is small so that Ka 1 the limits and to become:

EFJKA (14) E 30 (K x iK o 1201e a S111 neglecting terms of order higher than 7r '0 l s sin (Isvolts/meter (27) 7'0 To where rt is the distance from the origin (center I of loop). "*=J i 00$ 9 S111 NOW LOOP CIRCUMFERENCE MULTIPLE OF WAVE- A =Aa: S111 +Ay C05 9 (15) LENGTH and When the circumference is an integral mul- 46:01.3 cos +111 sin (1,) cos 0 (16) tiple m of a wavelength the above infinite series expressions degenerate to a slngle term andwe The current distribution is given by have; V

N (Kw) (17) E =1r60f e- (m)(j) J,,, (m sin 0 cos s 29 The angle 1,0 between the radius vector to the E3=60rg e" (m)(j)"J,,. (m sin 0) cos 6 sin me volts/meter (30) current element andthe radius vector to the 2. Radiation resistance dist point P is en b t- I In general power is radiated in both polarizations. The power in each will be separately calculated.

, The Poynting Vector, or watts persquare meter The phase ang1e=Ka cos =Ka sin 0 cos (o) radiated, is given by n P E H-r1 12017 (31) at a great distance. Separating into its two parts We then obtain:

9,615,134 11 12 The radiation resistance is the total power per 3. Voltage induced in a receiving loop ampere squared radiated through a sphere. We T i shall call the two parts of this resistance R. and i i f gsfig g ggig (assummg sme wave Re. Then:

i cos (Ka 4:0) (45) 2 1r D I f P sin M 5 33 where #20 is the position angle, a the loop radius 10 0 0 and I f1rf21r Rg-I0 0 0 Pg S111 d0d (34:) 10 K- A l c Hence we obtain: I Let E and Ee be the horizontally and. vertically 2W 1 J 1 K 0 polarized field strengths of the wave coming in at R J; J; (Ka) S1112 Ka1r b the colatitud angle 0 and longitude angle Using the center of the loop as phase reference n J,. (Ka sin 0) the phase angle of the incoming wave is:

('-'j) W COS 71 X 'n=1 Ka cos (o) sin 0 (46) lconiugatelxsin edit (35) The component of E in the direction of the and a similar type of expression for R0. This element ad is may be written in the form: Ed, cos 47) F (0) The component of E6 in the direction of the ff 2 FAG) cos X element ad 0 is F00 .s E0 008 9 in (-o) [T g (9) cos Sm Maw (36) The voltages 11V and dVe induced in the elements b horizontall and verticall olarized where Few) is a function of 0 only, Fn*(0) its Waves argthereforez y y p complex conjugate and C a constant.

Due to the orthogonality of the Fourier series 60S o we can immediately integrate with respect to it (W cos 9 sin )Xad 1'Ka anew-1 0 tin and obtain: 50)

1r 2 J; [F0200 +2 FAG) Sin ode The total voltages induced are then given by.

I1 1r (37) t= f cos ('-'o) em M) we.

1 J (Kasin0) I J,J(Ka sin 0) 2 R=120(KG,) S1112 (Ka'lrh jl) 1% (Ka) S111 6010+; 0 W 8111 9d9' ohms It simplifies evaluation to change the variable of integration to uzcos 0. The Re part of the V E J' m mu mum resistance is obtained by a similar procedure and a a 0 cos -,e Sm (Q5 6 0 we have the following results for the two parts (52) of the radiated power per ampere squared:

SMALL LOOPS Proceeding in the same manner as for the When Ka 1 the limit of the above formulas transmitting case we obtain:

become: 1

area V=4E Ka sin (Ka'r) f 53 9+ R.,,=201e(Ko =3117o ohms 41 a J,. (Ka sin 0) R =401r (Ka) ohms (42) EH1) cos no] volts (53) VQ=4EQKQ Sill (Kavr) COS 6 "2:; W

sin 12 volts (54) LOOP CIRCUMFERENCE MULTIPLE OF A WAVE- L SMALL LooP ENGTH when the circ ference is a multiple m of a The voltage Vs induced in asmall loop is wavelength (Ka=m) 7O V.=jK1ra E sin 6 (55) 2 2-[ q /mfl (43) as found by taking the limit of the above expression for V as a approaches zero. +1 It will be noted that these expressions are t zI [J 1( /i 2)] u2du 4 identical with the transmitting field strength 7 formulae except for a constant multiplier.

atiana 13 l'4 L' OIR FE MULTIPLE ductor opposite to the end of said hollow portion WAVELENGTH thereof, thereby to provide a substantially uni- In a manner similar to t transmitting form directivity pattern in a plane substantially dition these formulas degenerate into: parallel to that of said conductive surface ele- V =E m \(j)"J (m sin cos nut (56) z ix 1 t t 1 d oop an enna arrangemen me u mg a )mJm1(m Sm 0) cos Sm (57) substantially plane conductive surface element. Uniform cuwent mom a conductor curved to lie on the circumference of a circle in a plane parallel to said conductive If we assume the current to be constant all surface element, said circumference bein at least around the loop we obtain: as great as one wavelength, said conductor being 'K 1' E jK r" cos 0 exp [j{Ka sin 0 cos o) ada, 5s)

b e- 2 a JK c To X J (Ka sin 6) E. S. units (59) 6O1rI0 R Ru (Ka)J (Ka sin 0) volts/meter 0 in meters (60) The radiation resistance becomes: hollow for at least one-half of the length thereof,

there being a gap in said conductor at one point f 2) (61) along the hollow portion, at least one support- -1 in member fixed to said conductive surface element and to said conductor on one side of the Half Circle half wavelmgm loop gap therein, a further supporting member in the By a process similar to that already shown for form of sheath conductor of a coaxial transmisa complete loop we obtain for a half circle loop sion line passing through and aflixed to said con- While I have illustrated a particular embodiductive surface element and connected to said ment of the present invention, it should be clearly conductor at a point on the circumference thereunderstood that it is not limited thereto since 0f removed from e p, Said Supporting many modifications may be made in the several P hfWmg a length eq al to an odd multiple elements employed and in their arrangement and lncludmg llmty Of a Q r i e Op it is th ef r contempmted by the appended wavelength, said coaxial transmission line havclaims to cover any such modifications as fall mg an I n r onduc r extending substantially within the spirit and scope of the invention. throughout the hollow P01131011 of Said curved What is claimed is: conductor and across said gap.

1. A loop antenna arrangement including a A 1 antenna arrangement mcludmg a substantially plane conductive surface element, conductlve Sumac? element, l elongated cona conductor curved to lie on the circumference ductor f to on the penmeter a closed of a circle in a plane parallel to said conductive geometncal figure m a plane substantlauy surface element Said circumference being twice allel to said conductive surface element, said cirthe operating wavelength, said conductor being cutnference bemg at as great the p hollow for at least one operating wavelength, atmg wavelength: 531d conductor bemg hollow there being a gap in Said conductor at one end for at least a portion of the length thereof, there of the hollow portion, a pair of supporting membemg gap m conductor at e point alo g hers fixed at one end to said conductive surface the hollow portlon, supportm? members element and at the other end to said curved each fixed at one end to Said cQnductlve Surface conductor on either side of the ga therein, a element and the other to sald elfmgated 0 further supporting member in the form of an z at least 9 0f supportmg members outer conductor of a coaxial transmission line g i Bald supportmg. memberihavmgf a passing through and aiiixed to said conductive eng equal to an Odd llt ple mcludmg un ty surface element and connected to said curved weraimg wavelength, a conductor at a point on the circumference thereof :3 i s? 2 31 2 g shiath conductor opposite said gap, said supporting members hav- S 1 co we sur ace 6 ement and an i inner conductor extending through one of said ing a length equal to an odd multiple includi g supporting members, the hollow portion of said unity of a quarter of the operating wavelength, arcuate conductor and across Said gap. said coaxial transmission line having an inner conductor extending through the hollow portion PHILIP CARTER of said curved conductor and across said gap and being connected to the end of said curved con- (Referen on f ll i page) REFERENCES CITED The following references are of record in th file of this patent:

UNITED STATES PATENTS Number Name Date Berndt Dec. 6, 1938 Cork Aug. 1, 1939 Finch May 16, 1944 McGuigan Dec. 18, 1945 10 Number Number 

